1. Field of the Invention
The present invention relates to a method for manufacturing slabs suitable for rolling long products, particularly wire, sectional steel, bar steel, rails or the like by means of a continuous casting plant with casting mold. The present invention also relates to a continuous casting plant with mold for carrying out the method.
2. Description of the Related Art
When casting slabs which are required for rolling long products, such as, wire, section steel, rod steel and rails, usually square billets and blooms are cast. The sizes of the square billets are in the dimensional range of between 60 and 200 mm, primarily about 100 mm, and the blooms have dimensions of, for example, 250.times.320 mm.
In continuous billet casting plants, casting is usually carried out with an open pouring stream between the distributor and the mold and with oil as lubricant. On the other hand, in continuous bloom casting plants, casting is carried out with submerged pouring pipes and casting powder. These continuous casting plants primarily are curved strand continuous casting plants with vertically arranged mold, wherein these plants, in turn, are to be subdivided in vertical plants, vertical bending plants and circular arc-type plants.
Moreover, to a certain but small extent, blooms are also cast in horizontal continuous casting plants. The slabs cast by means of these plants primarily are of special steels which in the casting state can only absorb small bending loads.
Depending on the dimensions of the slabs, the continuous casting plants described above are operated with a maximum operationally realistic casting speed of about 1.5-3.0 m/min.
Contrary to continuous billet and bloom casting plants, due to the round shape in the mold, particularly in the area of the meniscus, continuous round billet casting plants have higher casting speeds of 2-4 m/min. In addition to the possibility of providing an improved uniform slag lubrication and, thus, a more uniform and reduced heat removal with the use of a submerged pouring pipe with casting powder, round billet continuous casting plants also result in an improvement of the slab surface and the quality of the slab interior. However, round billets have up to now almost exclusively been used in seamless pipe plants and not in rolling mills for producing wire steel, rod steel or sectional steel. The reasons for this are the better storing and transporting possibilities of square billets or rectangular shapes in the furnaces arranged upstream of the rolling mill, such as continuous-type furnaces and walking beam-type furnaces. This is particularly true for already existing mini-mills or also integrated metallurgical plants which between the continuous casting plant and the rolling mill frequently operate a continuous-type furnace which is supplied through an intermediate storage.
A possible solution for the object of combining the advantages of a round continuous casting mold and a square billet is described in patents DE 4139242 and WO 93/04802. Another object of these inventions is to improve the internal quality of the slab by reducing the cross-section during the solidification underneath the mold in the area of the slab guide means. In this case, underneath the oval or round continuous casting mold, the slab is shaped by means of stands into a polygonal or billet shape. Three stands are required for this purpose, wherein, due to ruptures of the slab, the stands are very endangered especially underneath the mold, and wherein the stands increase the operating costs as well as the investment costs of the continuous casting plant. In addition, it is to be pointed out that with increasing distance underneath the mold, the slab shell becomes thicker and colder and is more difficult to shape as a result.